Remediation of Soddy-Podzolic Sandy Loamy Soils Contaminated by Sewage Sludge

The paper presents the results of a model experiment in the humus horizon of soddy-podzolic sandy loamy soil (Albic Retisol), which was saturated with sewage sludge until 1990. As a result, complex multi-element contamination with heavy metals has been formed, which persisted even after 30 years. The aim of this work is to study the possibility of remediating soils contaminated with sewage sludge using chemical and biological rehabilitation methods. A total content of heavy metals was determined after soil treatment with concentrated HCl + HNO3 acids in a ratio of 3 : 1, and the content of mobile compounds was analyzed in the CH3COONH4 extract with a pH of 4.8. The concentration of heavy metals was measured on an Agilent 5110 optical emission spectrometer using the ICP-OES method. The use of organic and mineral remediants, i.e., zeolite clinoptilolite, zeolite ZION, humic preparation Vibrostend, biochar, and compost, proved the possibility to reduce the heavy metal content in vetch (Vicia sp.) and flax (Linum sp.) plants and to increase their biomass by 20–30%. The distribution of heavy metals by plant parts has also changed—it has risen in roots and has decreased in the vegetative mass. It is shown that flax plants accumulate heavy metals insignificantly even on contaminated soils, and the ameliorants used in the experiments reduce the Cd, Zn, Cu, and Ni content in vetch plants by 40–50%. Options with clinoptilolite or ZION zeolites were more effective for vetch plants. The ameliorative additives were effective for flax and vetch plants, increasing their vegetative mass and reducing heavy metal content, which is especially important for the most toxic Cd compounds.